1. Field of the Invention
The present invention relates to a vertebral body spacer having a cylindrical inner body that is telescopically slidable into a coaxially arranged, sleeve-shaped outer body.
2. Description of the Prior Art
A vertebral body spacer having a cylindrical inner body that is telescopically slidable into a coaxially arranged, sleeve-shaped outer body is known from DE 296 16 778. In order to fix said vertebral body spacer in the desired position, it can be guided through the outer body into a thread embedded in the inner body. By arranging a plurality of holes and threads in the axial direction, the vertebral body spacer can be adjusted gradually. For the operating surgeon it is however very tedious to adjust the desired size of the vertebral body spacer and to then insert said screw into the corresponding thread, particularly because the outer and the inner body are very likely to become displaced with respect to one another and because it needs a certain dexterity to insert the fixation screw into the corresponding thread.
An implant for replacing missing vertebrae is known from U.S. Pat. No. 5,723,013 in which detent lugs are formed on an inner cylinder, said detent lugs engaging into mating detent notches provided on an outer cylinder. Both the inner cylinder and the outer cylinder are each provided with two coaxially oriented slots into which a securing and fixation element may be placed as soon as the two cylinders have been brought into coincidence. The detent lugs and notches are designed in such a manner that the inner cylinder can be pulled out of the outer cylinder against the resistance of the detent lugs.
During surgical operation however it is on the one side very difficult to bring the two cylinders into coincidence in order to position the securing element and on the other side to pull the inner cylinder out of the outer cylinder against the force of the detent lug to correct the overall height of the implant.
The document EP 1 080 703 describes a telescopically extendable vertebral body spacer comprising a cylindrical inner body and a sleeve-shaped outer body that is coaxial with said inner body, said inner body being telescopically slidable into the outer body. A plurality of detent lugs arranged in four rows are provided on the outer side of said inner body, whilst at the inner side of the outer body there are provided detent notches that are also disposed in four rows, detent lugs and detent notches being designed to mate together. Between two neighboring rows of detent lugs, or rows of detent notches respectively, there is provided a free space so that the detent lugs of the inner body are adapted to be brought into the corresponding free space of the outer body while the inner body is being telescopically slid into the outer body. Once the inner body is in the desired position with respect to the outer body, the inner body (or the outer body) is pivoted to some degrees so that the detents lugs are inserted into the detent notches. In cannot be excluded that with time the inner body will pivot back and will be pushed telescopically further into the outer body as a result of the large face action thereon, which is not desired.